Atrial and ventricular demand pacer with separate atrial and ventricular beat detectors

ABSTRACT

An atrial and ventricular pacer in which competition between spontaneous atrial activity and atrial stimulation is prevented. In the conventional type atrial and ventricular pacer, the detection of a QRS wave re-starts both the atrial and ventricular timing circuits, but spontaneous atrial activity does not inhibit the generation of an atrial stimulating pulse. In the description of an illustrative embodiment contained herein, by preventing the generation of such a pulse when a spontaneous atrial beat is detected the batteries have a longer life.

United States Patent 11 1 Berkovits ATRIAL AND VENTRICULAR DEMAND PACERWITH SEPARATE ATRIAL AND 1 VENTRICULAR BEAT DETECTORS Inventor: BarouhV. Berkovits, Newton Highlands, Mass.

American Optical Corporation, Southbridge, Mass.

Filed: Dec. 6, 1971 Appl. No.2 205,195

Related US. Application Data ['73] Assignee:

1969, Pat. No. 3,661,158.

52 US. Cl 1 References Cited UNITED STATES PATENTS Continuation-impartof Ser. No. 884,825, Dec. 15,

128/419 P, 128/421 Int. Cl A6111 1/38 Field of Search 128/419 P, 421,422

3,593,718 7/1971 Krasner et al. 128/419 P 1451 July 24, 1973 3/1972Greatbatch 128/419 P 3/1969 Keller, Jr 128/419 P P m w xamin -iwilmfim!" 1 Attorney William C. Nealon, Joel Wall et al.

7 Claims, 4 Drawing Figures 40 I0 El 15 1 ATRIAL DEMAND AB VDVENTRICULAR DEMAND 4 STIMULATDR DETECTOR DETECTDR STIMULATOR PatentedJuly 24, 1973 ATRIAL DEMAND STINULATDR 600IFI/ VENTRICULAR DEIIANDSTIIIULATDR I I soon;

I vinnucuua FIRING LEVEL ATRIAI.

FIRING LEVEL name LEVEL ATIIIAL FIRING LEVEL VENTRICULAR 40 I0 E/ 30/ 5'mm 0mm) A a v 8 VENTRICULAR I mama srmumon DETECTOR DE more R snnumoaATRIAL AND VENTRICULAR DEMAND PACER WITH SEPARATE ATRIAL AND VENTRICULARBEAT DETECTORS This application is a continuation-in-part of mycopending application, S er. No. 884,825, filed on Dec. 15, 1969 andwhich has matured into U.S. Pat. No. 3,661,158.

This invention relatesto atrial and ventricular pacers, and moreparticularly to such pacers in which competition between spontaneousatrial activity and atrial stimulation is prevented.

There are many patients who require an atrial and ventricular pacer, asopposed to the more usual ventricular pacer. In demand pacers of thelatter type, a detector monitors the spontaneous ventricular beating ofthe heart; if too long a time interval has elapsed since the last beat,a stimulating pulse is generated to trigger the ventricular beat. Inpacers of the former type, an additional circuit is provided forgenerating atrial stimulating pulses to compensate for irregular atrialactivity. To maintain synchronism between the two pulsing circuits, asdisclosed in my above-identified application, every ventricular beatwhether natural or stimulated causesthe atrial timing period to re-starttogether with the (longer) ventricular timing period. Following anyventricular beat, an atrial stimulating pulse is generated a short timeafter the next atrial beat should occur. The atrial stimulating pulse isgenerated even if a natural atrial beat occurs. Thereafter, aventricular stimulating pulse is generated, but only if a naturalventricular beat does not occur within a predetermined time intervalsubsequent to the previous ventricular beat.

As explained in my co-pending application, if an atrial stimulatingpulse is generated following an atrial contraction, that is, during therefractory interval of the atria, it has no effect on the beating actionof the patients heart. It is only.the generation of a ventricularstimulating pulse during the refractory interval of the ventricles thatcan be dangerous. For this reason, the detection of a spontaneousventricular beat inhibits the generation of the ventricular stimulatingpulse which would otherwise soon occur. But atrial stimulating pulsesare not inhibited. In fact, even if the heart beats perfectly, in theconventional type atrial and ventricular pacer, an atrial stimulatingpulse is generated during every heartbeat cycle. Of course, the timingof the atrial pulse generator is keyed to the ventricular beats so thatat all times both pulsers and the natural heart activity remain insynchronism.

In my co-pendiug application, I described the possibility of detectingan atrial contraction and in response thereto re-starting the atrialtiming period. However, it was believed to be difficult to detect anatrial contraction (or, more accurately, the atrial depolarizationsignal), and for that reason an atrial beat detector was no provided inmy earlier pacer.

It is a general object of my invention to provide an atrial andventricular pacer of the prior art type but in which the detection of anatrial beat inhibits the generation of the atrial stimulating pulsewhich otherwise would be generated soon thereafter.

In accordance with the principles of my invention, a conventional typeECG wave detector is provided 'to detect atrial depolarization signalsin the prior art type atrial and ventricular pacer. The detection of aventricular beat still re-starts the timing of the atrial pulsegenerating circuit (along with that of the ventricular pulse generatingcircuit), but now the atrial pulse generator is also inhibited fromproducing an atrial simulating pulse whenever a spontaneous atrial beatis detected. The major advantage of this design is that atrialstimulating pulses are not generated when they are not needed; the drainon the battery is reduced and the pacer has to be replacedlessfr'equently. (Although some atrial contractions may not be detected,that simply results in the type of operation described in my copendingapplication. It is for each atrial beat which is detected that the drainon the battery is reduced.)

It is a feature of my invention to provide an atrial beat detector in anatrial and ventricular pacer, the detection of an atrial beat resultingin the re'starting of the atrial timing period and the inhibition of thegeneration of the atrial stimulating pulse which otherwise would begenerated.

Further objects,features, and advantages of my invention will becomeapparent upon consideration of the following detailed description. inconjunction with the drawing in which: i

FIG. 1 depicts schematically the atrial and ventricular pacer disclosedin my co-pendling application;

FIG. 2 consists of timing waveforms which will be helpful inunderstanding the operation of the circuit of FIG. 1; I

FIG. 3 depicts schematically the illustrative embodi ment of theinvention; and

FIG. 4 consits of timing waveforms which will be helpful inunderstanding the operation of the circuit of FIG. 3.

FIG. 1 depicts three circuit blocks, the details of which are disclosedin my co-pending application. Ventricular demand stimulator 10 applies aventricular stimulating pulse, on ventricular electrodes El and E2, 800milliseconds after the previous ventricular beat, whether spontaneous orstimulated. A ventricular beat also results in the appearance of a pulseon the electrodes which is extended to ventricular beat (VB) detector20. The VB detector extends a signal over conductor 40 to theventricular demand stimulator, in response to the detection of aventricular beat, to inhibit the generation of the next ventricularpulse which otherwise would be generated and to control the start of anew 800-millisecond timing interval. Atrial demand stimulator 30 isprovided to extend an atrial stimulating pulse to electrodes E3 and E4.The atrial stimulator timing period starts together with the ventircularstimulator timing period, the VB detector output being extended to bothpulse generators. However, the timing period of the atrial stim ulatoris 600 milliseconds rather than 800 milliseconds.

FIG. 2 depicts the operation of the pacer during seven heartbeat cycles.The letters R and P indicate respectively spontaneous ventricular andatrial contractions which occur during the seven cycles. The letters VSand AS identify respectively the generations of ven tricular and atrialstimulating pulses. Since the detection of a ventricular beat re-startsthe atrial timing period, and the atrial timing period is 600milliseconds, the time interval between each spontaneous ventricularbeat and the next atrial stimulating (AS) pulse is 600 milliseconds asshown. The notation 600(F) is used to indicate that the intervalseparating any spontaneous ventricular contraction and the next atrialstimulating pulse is fixed. Similarly, since each stimulatingventricular beat (VS) results in VB detector 20 energizing its output 40to re-start both timing periods, the interval between each VS pulse andthe next AS pulse is similarly 600 milliseconds and is shown by thenotation 600(F).

In the absence of a spontaneous ventricular beat, a ventricularstimulating pulse is generated 800 milliseconds after the previousventricular beat under control of ventricular demand stimulator 10.Since the interval is always 800 milliseconds, the notation 800 (F) isused to indicate the time between a spontaneous ventricular beat (R) andthe next ventricular stimulating (VS) pulse if such a pulse isgenerated, and the time interval between one ventricular stimulatingpulse and the next ventricular stimulating pulse in the absence of anintervening spontaneous ventricular beat. Finally, in the example shownin the drawing, it is assumed that a spontaneous ventricular beat (R)occurs 700 milliseconds after a previous ventricular beat, whetherspontaneous (R) or stimulated (VS). Consequently, 700 millisecondsseparate each R-R pair or VS-R pair. Since each of these time intervalsis not fixed, and instead is a function of the condition of the patient,the letter F is not used together with the 700-millisecond designations.

, In the circuit of FIG. 1, as shown in FIG. 4 of my copendingapplication, two capacitors are provided to control the 600-millisecondatrial timing period and the 800millisecond ventricular timing period.Each capacitor charges from an initial value toward a respective firinglevel. It takes 600 milliseconds for the atrial capacitor (57 in myco-pending application to reach the atrail firing level, at which timean atrial stimulating pulse is generated, the capacitor is dischargedand a new timing interval begins; it requires 800 milliseconds for theventricular timing capacitor (57) in my copending application to reachthe ventricular firing level, at which time a ventricular stimulatingpulse is generated, the capacitor is discharged and a new ventriculartiming period begins. Both capacitors are discharged and new timingperiods begin when either a spontaneous ventricular beat (R) is detectedor a ventricular stimilating (VS) pulse is generated. The two sawtoothwaveforms depict the respective capacitor voltage waveforms. The littlearrows directly above the peaks of the waveforms indicate when, for theseven illustrative cycles, atrial and ventricular stimulating pulses aregenerated as a result of the voltages of the respective capacitorsrising to the respective firing levels.

With respect to the ventricular capacitor voltage waveform, the voltageacross the capacitor has sufficient time to rise to the ventricularfiring level only in the absence of a spontaneous ventricular beat.Consequently, it is only at the end of each of cycles 3 and 4 that aventricular stimulating pulse is generated. In the case of the atrialcapacitor, however, the voltage across it always reaches the atrialfiring level 600 milliseconds after the detection of a spontaneousventricular beat (R) or the generation of a ventricular stimulating (VS)pulse. Consequently, an atrial stimulating pulse is shown as occuringduring every cycle. Immediately after the generation of an AS pulse, theatrialcapacitor voltage starts to rise. But the QRS detector causes thecapacitor to be discharged at the end of each cycle when a spontaneousventricular beat (R) is detected, or a ventricular stimulating (VS)pulse is generated. The

capacitor then starts to charge again and the atrial firing level isreached 600 milliseconds later.

The circuit of FIG. 3 is similar to that of FIG. 1 except that atrialbeat (AB) detector 50 is provided. The atrial electrodes E3 and E4 areconnected to inputs of the AB detector. The AB detector is similar tothe VB detector 20, and may in fact be identical. Although it wasbelieved to be difficult to detect atrial beats (that is, the atrialdepolarization signal), this is no longer always true. The problem inthe past was that the atrial electrodes would shift slightly afterimplantation. But newer atrial electrodes which have become availablecommercially permit far more reliable detection of atrial depolarizationsignals.

The output of AB detector 50 and the output of V8 detector 20 are bothextended to respective inputs or OR gate 60, the output of which isextended to atrial demand stimulator 30. The only difference between thepacers of FIGS. 1 and 3 is that in the latter circuit the timing periodof the atrial demand stimulator is restarted whenever a spontaneousatria] beat is detected, as well as when a spontaneous ventricular beatis detected or a ventricular stimulating pulse is generated.

FIG. 4 shows the capacitor waveforms for the same seven heartbeat cyclesdepicted in FIG. 2. The major difference between the two timingsequences is that with the circuit of FIG. 3 each spontaneous atrialbeat (P) re-starts the atrial timing period. It is only in the absenceof a spontaneous atrial beat, during heartbeat cycles 4, 5 and 7, thatatrial simulating (AS) pulses are generated. While the ventricularsawtooth waveforms are thus the same in FIGS. 2 and 4, the atrialsawtooth waveforms are considerably different. In FIG. 4, the atrialfiring level is reached during only three of the seven heartbeat cycles.In general, because an atrial stimulating pulse is not generated by thepacer of FIG. 3 when a spontaneous atrial beat is detected, there isreduced battery dissipation. This contributes to extended life of thepacer.

Although the invention has been described with reference to a particularembodiment, it is to be understood that this embodiment is merelyillustrative of the application of the principles of the invention.Numerous modifications may be made therein and other arrangements may bedevised without departing from the spirit and scope of the invention.

What I claim is:

l. A pacer comprising terminal means for connection to a patients heartfor atrial stimulation, terminal means for connection to said patientsheart for ventricular stimulation, means for detecting an atrial beat ofsaid patients heart, means for detecting a ventricular beat of saidpatients heart, means responsive to the operation of said ventriculardetecting means for generating an electrical stimulus on saidventricular terminal means following a first predetermined time intervalafter the last detected ventricular beat only of said patients heart,means for generating an electricalstimulus on said atrial terminal meansfollowing a second predetermined time interval after the lastventricular beat only of said patients heart, and means for preventingthe generation of an electrical stimulus on said atrail terminal meansresponsive to the detection of an atrial beat of said patients heartduring said second predetermined time interval.

2. A pacer in accordance with claim 1 wherein said first predeterminedtime interval is longer than said second predetermined time interval.

3. A pacer in accordance with claim 2 wherein said second predeterminedtime interval is shorter than a probable minimum interval betweensuccessive ventricular beats of said patients heart and is longer than aprobable maximum interval between a ventricular beat and the next atrailbeat of said patients heart.

4. A pacer in accordance with claim 3 wherein said first predeterminedtime interval is longer than the usually-occurring interval betweensuccessive ventricular beats of said patients heart.

5. A pacer comprising terminal means for connection to a patients heartfor ventricular stimulation, terminal means for connection to saidpatients heart for atrial stimulation, a first timing circuit means forgenerating an electrical impulse on said ventricular terminal means, asecond timing circuit means for generating an electrical impulse on saidatrial terminal means, means for detecting a ventricular beat of saidpatients heart and responsive thereto for resetting both of said firstand second timing circuit means, and means for detecting an atrial beatof said patients heart and responsive thereto for resetting said secondtiming circuit.

6. A pacer in accordance with claim 5 wherein the period of said firsttiming circuit means is longer than a probable maximum interval betweentwo successive ventricular beats of said patients heart.

7. A pacer in accordance with claim 6 wherein the period of said secondtiming circuit means is longer than a probable maximum interval betweena ventricular beat and the next atrail beat of said patients heart. v

1. A pacer comprising terminal means for connection to a patient''sheart for atrial stimulation, terminal means for connection to saidpatient''s heart for ventricular stimulation, means for detecting anatrial beat of said patient''s heart, means for detecting a ventricularbeat of said patient''s heart, means responsive to the operation of saidventricular detecting means for generating an electrical stimulus onsaid ventricular terminal means following a first predetermined timeinterval after the last detected ventricular beat only of saidpatient''s heart, means for generating an electrical stimulus on saidatrial terminal means following a second predetermined time intervalafter the last ventricular beat only of said patient''s heart, and meansfor preventing the generation of an electrical stimulus on said atrailterminal means responsive to the detection of an atrial beat of saidpatient''s heart during said second predetermined time interval.
 2. Apacer in accordance with claim 1 wherein said first predetermined timeinterval is longer than said second predetermined time interval.
 3. Apacer in accordance with claim 2 wherein said second predetermined timeinterval is shorter than a probable minimum interval between successiveventricular beats of said patient''s heart and is longer than a probablemaximum interval between a ventricular beat and the next atrail beat ofsaid patient''s heart.
 4. A pacer in accordance with claim 3 whereinsaid first predetermined time interval is longer than theusually-occurring interval between successive ventricular beats of saidpatient''s heart.
 5. A pacer comprising terminal means for connection toa patient''s heart for ventricular stimulation, terminal means forconnection to said patient''s heart for atrial stimulation, a firsttiming circuit means foR generating an electrical impulse on saidventricular terminal means, a second timing circuit means for generatingan electrical impulse on said atrial terminal means, means for detectinga ventricular beat of said patient''s heart and responsive thereto forresetting both of said first and second timing circuit means, and meansfor detecting an atrial beat of said patient''s heart and responsivethereto for resetting said second timing circuit.
 6. A pacer inaccordance with claim 5 wherein the period of said first timing circuitmeans is longer than a probable maximum interval between two successiveventricular beats of said patient''s heart.
 7. A pacer in accordancewith claim 6 wherein the period of said second timing circuit means islonger than a probable maximum interval between a ventricular beat andthe next atrail beat of said patient''s heart.